A Sea kayak is a kayak developed for the sport of paddling on the open waters of the ocean.

Typically a seaworthy small boat with a covered deck and the ability to incorporate a spraydeck.

Modern sea kayaks come in a bewildering array of materials and designs. Along with the common fiberglass, rotomoulded polyethylene and kevlar, there are more exotic materials, such as carbon fiber and Royalex, and hand-built systems, such as skin on frame (canvas, dacron or other fabric over a lattice-like framework) and "stressed skin" plywood. Designs are divided into categories based on the shape from bow to stern and on the shape of the hull in cross-section. Overall shapes are:

• Symmetrical: the widest part of the boat is exactly halfway between bow and stern.
• Fish form: the widest part is forward of the midpoint.
• Swede form: the widest part is aft (in back) of the midpoint.

Hull shapes are categorized as:

• Chine: hard chine, medium chine, soft chine
• Flat bottom
• Semi-round bottom or, even, round bottom.
• Shallow V-bottom
• Combinations of the above.

The sport of sea kayaking is increasing in popularity. It combines much of the appeal of hill-walking with a maritime aspect, few access issues and an almost infinite area to enjoy.